[Gmsh] Reversing mesh normals

[Jeremy Theler]

If you go through the post-processing the .msh file you can also change
the ordering of the nodes in order to get the normals in the direction
you want.


-- 
Jeremy Theler
www.seamplex.com



On Tue, 2017-01-24 at 12:15 +0000, DILASSER Guillaume wrote:
> Hello Mark,
> 
>  
> 
> Not sure about this, but the reverse all normal command could just be
> post-processing. This would explain why it is not saved in you mesh
> file once you update it. I would suggest using the Reverse Line
> { line_id } / Surface { surface_id } / “*” command. What it does is
> reverse the node ordering within a given line, surface, or globally.
> Since node ordering dictates normal orientations, you should get what
> you want.
> 
>  
> 
> Additionally, there is to my knowledge no way of generating Physical
> Groups of directly on meshes. Yet, I see two work-arounds. Solution
> one, is to re-process your msh file outside of Gmsh.  A msh file has a
> $PhysicalNames section that you can add by hand to define your groups
> but then you would have to tag each element belonging to the group
> individually in the $Element section. That could work but that is
> certainly not practical, see documentation on MSH file format for more
> information.
> 
>  
> 
> Second possibility, have a look at STL remeshing example on the wiki
> (user: gmsh, password: gmsh). This could be a way to re-create a
> geometry based on your mesh, apply the Physical group and finally
> re-save the geometry with the groups.
> 
>  
> 
> Hoping this was useful,
> 
>  
> 
> Guillaume Dilasser
> 
>  
> 
> De : gmsh [mailto:gmsh-bounces at ace20.montefiore.ulg.ac.be] De la part
> de Mark Smith
> Envoyé : lundi 23 janvier 2017 16:52
> À : gmsh at onelab.info
> Objet : [Gmsh] Reversing mesh normals
> 
> 
>  
> 
> Hi Gmsh users,
> 
> I have a gmsh format mesh produced in pointwise which I load into
> gmsh. I wish to reverse the direction of the surface normals on the
> mesh which I do by options>mesh>color>Reverse all normal, if I set
> mesh.normals to some non zero value the normal vector is displayed on
> the surface mesh and reverse all normal does indeed reverse the
> vectors direction BUT if I save the mesh out to gmsh msh format with
> the normals reversed then load it back into gmsh the normal direction
> is the same as the original, am I doing something wrong or is what I
> want to do not possible?
> 
>  
> 
> Also Is it possible to only reverse the normals on certain mesh
> surfaces rather than all?
> 
>  
> 
> Is there a way to define Physical groups on a mesh rather than on
> Geometry if one only has a mesh?
> 
>  
> 
> Thanks in advance
> 
> Best regards
> 
> Mark
> 
>  
> 
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